Traditionally, various fluorocarbon gases (freon) have been used as foaming agents to obtain foamed articles having high expansion ratios. The use of freon is, however, gradually restricted in view of its harmful influence to the environment, such as depletion of the ozone layer.
While there have been studied various foaming agents to take the place of freon, they are associated with difficulties in obtaining an article foamed in a uniform fashion and having a high expansion ratio. Accordingly, a method for producing, without using freon, a uniformly and finely-foamed article having a high expansion ratio, which causes no environmental problems such as depletion of the ozone layer, or a foamable composition capable of providing such foamed article is demanded.